Automatic telephone system



Nov. 1, 1932.

c. E. STEVENS ET AL 1,886;065

AUTOMATIC TELEPHONE SYSTEM Filed Sept. 8, 1950 2 Sheets-Sheet 1 U D I] D U El [1 FIG. 2

LJ MRF CH; 3mm JOSQNNU .SCHOONEMAN N v 1, 1932. c, E. STEVENS ET AL 1, 6

AUTOMATIC TELEPHONE SYSTEM Filed Sept. 8, 1930 2 Sheets-Sheet 2 INVENTOR CHARLES E. STEVENS JOHANNUS c. SCHOONEMAN Patented Nov. 1 1932 CHARLES EDWARD scnnvnns AND JOHANNUS CORNELIS SCHOONEMAN, or ANTWERP,

BELGIUM, ASSIGNOBS TOINTERNATIONAL STANDARD ELECTRIC CORPORATION, OF

NEW YORK, N. Y., A OQRPOEATION (3F DELAWARE AUTOMATIQ TELEPHONE SYSTEM Application filed September 8, 1930, Serial No. 480,460, and in Great Britain October 9, 1929.-

This invention relates to switching arrangements for automatic or semi-automatic telephone systems and more particularly to arrangements of the kind in which selector switches are operated under the control of control or auxiliary switches which are common to a plurality of selector switches.

According to one feature of the invention a control switch common to a plurality of selector switches is adapted to respond to two digits of a wanted number and to cause the advance of a selector switch first to a wanted group of lines and then to a wanted line or subgroup of lines within said selected group under the control of marking potentials applied to marking wires which are connected between the ban is of said selector switches andsaid control switch in such a manner that correct marking is efiected in response to both digits without moving the control switch to a predetermined position after the first marking operation has been terminated.

According to another feature of the invention a control switch common to a plurality of conversation selectors is adapted to perform two selective movements, 2. first to mark a wanted group of lines and a second to mark a wanted line or subgroup of lines in said wanted group, both movements being performed under the control of a mechanism to which the control switch sends revertive impulses.

According to a still further feature a control switch common to a plurality of selector switches is adapted to hunt for a selector switch which has been taken for use and is also adapted to perform the two marking operations specified in the preceding paragraph.

The invention is described as applied to a system such as is described in our copending application Ser. No. 37 0,673, but it is to be understood that the invention is not limited to such arrangements and numerous modifications will readily occur to those versed in the art. It will be evident for example that the invention is equally applicable to circuits using ,step-by-step switches operated by forward impulses.

In theaccompanying drawings Fig. 1 shows a final finder circuit.

Fig. 2 shows a final finder control circuit.

Fig. 3 shows the method of wiring between the final finder switch banks, and the final finder control switch banks.

To make a complete circuit diagram Fig. 2 should be placed beneath Fig. 1.

The arrangement of the bank contacts of the final finder switch, and the final finder control switch as shown in Fig. 3 will first be described.

These switches are of similar construction and have semi-circular banks arranged in levels of 51 points in each.

The upper four levels 6 and (Z shown in the figure are associated with the final finder switch, the two levels (Z being used for P. BJX. hunting and will be described later.

These two levels are wiped over by'two single ended brushes set 180 apart, one brush wiping over the lower level during one-half revolution, and the other brush over the upper level during the other half revolution.

The two levels 6 are the line marking contacts a marking potential being applied to one of these contacts in accordance with the position to which the control switch has been set, whereupon the brushes of the final finder are advanced to find this marked contact.

As will be seen the lower level of these two levels contains the marking contacts of the lines 00 to 49, and the upper level the marking contacts of the lines to 99. The brushes are arranged as in levels (Z.

The lower four levels in Figure 3 show the arrangement of the final finder control switch bank.

These control switches serve ten regular final finder switches, and the first ten contacts in the levels it and 2' of the control switch bank are wired to these ten final finders for the purpose of allowing the control switch to attach itself to the final finder which has been selected by a preceding group finder switch. The method. of wiring is shown clearly in Fig. 2.

The 14th and 15th contacts in the levels f, h and 2' and every subsequent third'and fourth contact in these levels are connected together and are wired to the marking terminals in levels e of the final finder switch.

The contacts in levels f and h are wired to the tens markin contacts in level 6 of the final finder SWltll, and the contacts of level i are connected to the units marking contacts in the same level.

The 13th and 14th contact in level 9 and eqery subsequent third and fourth contact are connected together and grounded. These contacts are the revertive impulse contacts and send the grounded revertive impulses back to the register to count out the digits trains during the advance of the control switch.

Each of these levels are wiped by single ended brushes which wipe over the contacts one in each half revolution.

The method of wiring as shown in the N has been developed so as to reduce the time of units selection, and arranged so that when the control switch has to make a maximum number of steps the final finder makes a minimum, and vice versa.

For instance to reach the terminal 99 the brushes of the final finder after reaching the beginning of the tens group have to advance nine steps whereas the control switch advances two steps to mark the ninth terminal in thetens group over brush 2'. 7

n the other hand to mark the terminal 11,.after the final finder has reached the tens up, it is necessary for the control switch to be advanced ten subsequent steps to mark the first terminal in that group. It will be seen therefore that the two switches are arranged to interact to minimize the time of units selection.

The progress of a normal call will now be .A' tree final switch is characterized by a low resistance battery potential on its third wire C over a circuit from battery at contact l of relay ECR of the final control circuit 2), common wire, resistance B Fig. 1). Busy jack BJ of the final switch c rcuit contact 2 of relay FRI, contact 3 of relay BB3, contact 4 of relay F112.

A searching preceding group finder such as explained in the copending application referred to will stop due to this low battery potential, and subsequently the fundamental circuit from the register will be extended to thefinal finder switch, whereupon a battery potential is provided from the register over the A wire, contact 2 of relay F7'2, rela Aer to ground. Relay A01" operates over this circuit and at its contacts operates relay Ear over an obvious circuit. Relay Amat its contact also causes the final control switch to be advanced to find the'selected final finder over a circuit extending from battery at drive magnet PC of the control switch,

contact 1 of relay G01, contact 5 of relay Mc'r contact of relay Ber, contact 3 of relay For, contact 1 of relay Dar, to ground at contact of relay Aer. Immediately the switch becomes off normal the off normal contacts are operated in parallel with the contacts of relay Acr, to provide holding ground after relay A01 has been released.

At contact 1 of relay Ecr, the battery marking the 0 wire of all the free final switches associated with the control circuit is disconnected, marking that group busy to all searching group finder switches. This same contact causes the control circuit busy lamp to be illuminated.

Contact 4 of relay E01- prepares the circuit of relay Bc'r via contact 2 of relay F or.

The control switch advances until its brush encounters the contact associated with the seized final switch, whereupon the battery or the A wire of the fundamental circuit is extended to relay Bar, and thence to ground over the reviously described circuit.

Relay or at its contacts disconnects the circuit of the control switch drive magnet PC to stop the advance of the control switch, and completes a circuit for relay Frl (Fig. 1) from ground on contact of B01, wiper and terminal 2 of the control switch, relay FRl to battery.

Relay F r1 operates and locks over its contacts 2 to the ground on the 0 wire via contact 3 of relay F R3, contact 4 of relay FEE applied from the preceding switch. At contacts 3 and 4 relay Frl prepares the circuits of relays F7'3, and Ftr, respectively. At contacts 5 of relay Frl an obvious circuit is closed for the relief relay F1'4, this latter relay operates relay Fcr at contacts 1, whereupon relay Bcr de-energizes.

At contacts 1 of relay Frl a circuit is completed for the outstepping relay in the register and relay D01- in the control circuit over the B wire of the the fundamental circuit.

Relay Dar operates in this circuit and at contacts 1 recloses the circuit of the control switch drive magnet PC.

The control switch advances until the brush 9 encounters the 1st earthed contact in its lead whereupon a grounded revertive impulse is sent back to the register over the B wire via contact 2 of relay Dar, short circuiting the stepping relay therein to count out the tens register. Relay Dar is retained operated by this ground while the brush 9 is passing over the grounded contact.

Thecontrol switch continues to advance and at each 3rd and 4th contact sends a revertive impulse back to the register. The numbering scheme is so arranged that the revertive impulses are complementary to a base of 11.

When the tens register switch in the register controller is counted out the fundamen tal circuit is opened and as soon as brush g leaves the grounded contacts relay Dar deenergizes.

At contacts 3 of relay Ger a short circult is placed across relay Yer, the ground on one side of relay Y0?" being the initial operating earth of relay G01 the circuit of which has previously been traced, while ground is applied to the other side over contacts 3 of relay G01, contacts 3 of relay X01", contacts 2 of relay For, contacts 4 of relay E0? to ground. At contacts 4 of relay G01" a circuit is closed for the final finder driver magnet PF, from battery, drive magnet PF, contacts 3 of relay 1W4, common Wire, contact 4 of relay L01, contact 1 of relay H01". A circuit is prepared for relay H0?" at contacts 5 of relay G07,

' from battery, relay H01, contact 4 of relay Pm", contact 4 of relay Mm", contact 3 of relay L01", brush 7" of the control switch and the contact on which it has been set, thence to a whet the particular tens contact in arc e of the final finder switch.

The brush 6 of the final finder advances until it encounters this whetted contact, when relay H0?" is operated from ground at contact 4 of relay F1 4, brush and contact 6 of the final finder, thence over the circuit previously traced. At contact 1 of relay H01" the circuit for the final finder is disconnected, and a. circuit is closed for relay L01". At contact 3 of Law a holding circuit is established for relay Her.

Meanwhile the fundamental circuit from the register has been re-established and relay Dcr re-operates.

It will be remembered thatrelay Yer was short circuited at contact 1 of relay Der normal, and when relay Dar operates this short circuit is removed and relay Y0?" is allowed to operate in series with relay G07".

At contacts 2 of relay Yo?" an obvious circuit is closed for relay I07", and at contacts 1 a circuit is prepared for relay M02. Relay Icrat'contacts 1 closes a circuit for relay Jar.

Due to the operation of relay Dar, and provided that the final finder has found the marked tens group, that is, when relay L07 operated, a circuit is closed for PC control switch drive magnet from battery, drive magnet PC, contact 1 of relay Lcrl, contacts 5 of relay M07", contacts 1 of relay D07 1, to ground at the off normal contacts of the switch.

The control switch now starts to rotate from where it was standing after the tens selection, and brush 9 in passing over the grounded terminals sends back revertive impulses to the register to count out the units train. When the register has counted out the units train and the brush 9 has passed over the grounded terminal relay D01" de-energizes as before and at contactl disconnects the circuit of the drive magnet PC, and connects the circuit for relay M02, from battery relay Mm", contact 1 of relay Yer, contact 2 of relay Yer contacts 3 of relay For. Relay Mar looks over its contacts 1 to the ground at contact 3 of relay Ear, via contact 2 of relay For. At contacts 2 and 4 of relay Mar, the relay H01 is connected to the brushes h and 2' respectively, to whet the selected units contact in the are e of the final finder.

Unless the first line in a group is the Wanted line whenrelay Mar operated relays Her and L07 will be released as no ground will be found by the brushes it or c", and the ground at contact 3 of relay L07 locking relay Her is disconnectedat contact 4 of relay M01. The circuit for the final finder drive magnet is therefore closed over the path previously traced, and the final finder rotates until the brush e encounters the terminal connected with battery via H07 relay. Relay H01" thereupon operates from the ground applied at contact 4 of relay Fr4. At contact 1 of relay Her the circuit for the drive magnet PF is opened, and the circuit for relay L0? is completed as before.

lVhen relay H01" and L01" energized a circuit is completed for relay P07 from battery relay Per contacts 2 of'relay Gm", contacts 1 of relay Par, contacts 3 of relay M01, contacts 2 of relay L01", contacts 1 of relay Her, over contact 4 of G01 to ground. 7

Relay P01" is slow to operate and therefore will not operate during the short time interval that its circuit is completed prior to relays Hc-r and L01 de-energizing and the unit selection commencing. Relay P07" looks over its contacts 1 via contacts 2 of relay G01 At contact 2 and 4 of relay Per the circuit of relay Hcr via the brush it or 11 is disconnected, but another circuit is established over contact 4 from the grounded brush (Z of the final finder via the resistance R1 and contact 2 of relay F14. The operating ground for Par is now extended over its contact 3 of relay Par, relay X01" to battery. Relay Xcr therefore operates and locks to ground over its contact 3, contact 2 of relay F or, and contact 4 of relay E07". At contact 3 of Yer the hold circuit for relays G02" and Y0?" is opened. These relays release and by doing'so release relay 10?, and P01", which in turn release relays Hcr, L01 101*, and J or. Relays Yer, I00, and J02", however are slow to release and a. considerable time interval will occur before these relays relapse. Relay Xe)" at con tact 1 extends ground over resistance R3, contact 4 of relay F7 1, relay Ft'r, to brush 0 which is resting on the test terminal of the called line. If the called line is free a battery potential is found on the test terminal applied via the cut off relay Cor in the line equipment. Relay F231- operates in series with this. Contact 1 of relay Fir closes an obvious circuit for relay F92.

Contacts 2 and 3 of relay F7 2 extend the A and B wires of the fundamental circuit to contact-.1 of relay Fr2.

the 'geccding switch is extended to hold relay ts :md'relay Cor, and disconnects the circuit of relay F r1. Relay Frl does not relapse immediately as a holding circuit is provided over contacts 1 of relay J01- which beihgfllnwitoreleise has not yet relapsed. Contact l of "relay F12 opens the circuit of the b tone the application of which will be delater,and prepares for the applicatioh current to the called line.

When relay I01 finally relapses aground is paced over its back contact, contact 4 of relay X? contact 3 of relay Frl, relay Fr3, to battery. Relay Fr?) operates and locks to the ground on the a wire over its contact 4, contacts l and 2 of the tripping relay Frr. At contact 1 of relay F r3 the ringing current is applied to the calling line from earth battery; source of ringin current, relay FW',

elay F7? is :1 marginal relay and will not operate until the called subscriber removes his receiver. Tell taltainging tone is applied to the calling line throu h the condenser MFR. Contact 2 of relay r3 applies a return ground potential to! the ringing current.

Relay J 01' now relapses and opens the circuit ofzrelay Frl. Relay FM is thereupon released: disconnecting the control switch fromthe final finder. Relay FM releases relayl'lcr which in turn releases relays X0? and him. A homing circuit for the control switch is now established from battery at control-switch drive magnet PF, contact 1 of relay Gar, contact 5 of relay Mar, contact 1- of. relay Bar, Contact 3 of relay For, contactl of relay D01, to ground at the oil nornlalcontacts of the switch. The switch will therefore advance until it reaches its home '6!!! where the oil normal contacts w1ll be; broken. Relay Ear remains operated dnr' this homing operation to maintain the max circuit busy to any searching group finder. 'When the switch reaches its home this relay is released freeing the circuit for further use.

Resuming the consideration of a normal call'when the called subscriber answers, the current through the relay Fw' is increased and-thisrelay operates at contact 1 and 2 of relay F71',: the hold circuit for relay Fr3 istpened and this relay releases, and conneCEtheA and B wires through for speaking. circuit is now connected through with only two relays, Ftr and Fr? operated amliocked to the ground on the 0 wire. At theta-elimination of the conversation, that is when the calling party hangs up his receiver, the gmundon the 0 wire is removed allowing these relays and the cutoff relay in thecalled line equipment to release and restore the circuit to normal.

"If the called line is found engaged a ground will be met on the test terminal of the called line, and consequently relay Ftr is short circuited and will not operate. When relay Icr relapses ground will be passed over contact 4 of relay X01- to relay F1'3 which operates and locks as before. At contact 1 of relay Fr?) a busy tone will be ap lied to the callin parts from the grounded iiattery, the secon ary winding of the ousy tone transformer BT, contact 1 of relay 1W2, condenser MRF.

The release of the control circuit occurs as previously explained.

When the calling party hangs up his receiver the ground is removed from the third wire and relay F13 releases and restores the circuit to normal. The method of P. B. X. grouping will now be explained. It will be seen from a consideration of Fig. 1 that the d terminals of the lines associated with a P..B. X. group are grounded over the normal contacts of their cut-off relays C01- except the last line which is permanently grounded. When a line in a group is engaged the cutoff relay Cor will be operated and therefore the ground will be removed from its particular 0! terminal.

The final finder under the control of the control switch is advanced to the first line in the required P. B. X. group and if this line is engaged no ground will be found on the associated (1 terminal. Relays Her and Lcr are operated over the brushes 5 and i as before, but when For operates due to relay Dar falling away at the end of the units train no ground is returned from the d terminal over contact 4 of relay Par to hold these relays and they de-energize. A circuit is therefore established for PF final finder drivemagnet over contacts 4 of relay Lcr, and contacts 1 of Her, and the switch is advanced until a line is encountered which has a ground on the d terminal, this may be an intermediate disengaged line or the last line which may be either in an engaged or disengaged condition. The remainder of the call proceeds in a similar manner to a normal call which has previously been. described. If it is desired to provide night service on P. B. X. groups, a key NPBR incinded in the control circuit, when operated, permanently grounds the common wire leading to the d brush of the final finder. This enables each of the P. B. X. trunks to be called as an ordinary line by its individual number.

in the event of a toll call where the ringing current is applied from the toll exchange it is necessary for the relay Fri; to remain inoperative after the required linehas been tested and found to be free and relays Ftr and F 73 operated. To accomplish this result the register is so arranged that for a toll call, the fundamental circuit is reclosed for a certain time after the units impulses are finished. Relay D01- in the control circuit will therefore reoperate previous to the de-energization of relay I01.

Relay Dar at Contact 1 opens the holding circuit for relay Fr1,and this relay relapses disconnecting the control circuit previous to the ground being applied to relay F7 3 at contact 1 of relay 1G? in its normal position. The A and B wires therefore remain connected through to the toll operator, and allow for the direct passage of ringin If the called line is engaged relay F'r'l remains locked to the 0 wire, and relay F r3 is operated when relay 1C9 relapses. Busy tone is thereupon applied to the calling line, and the control circuit is released as previously described.

VJhat is claimed is:

1. In a telephone exchange system the conibination of a plurality of selector switches, a plurality of lines divided into groups and terminating in contacts of said selector switches, a control switch, means for transmitting digit impulses to said control switch, means under control of said control switch in response to two digit impulses to cause one of said selector switches to advance, first to a group of lines and then to a line within said group, comprising electrical connections between contacts in the selector switch and said control switch to which marking potentials are applied.

r 2. In a telephone exchange system the combination of a plurality of selector switches, a plurality of lines divided into groups and terminating in contacts of said selector switches, a control switch, means for transmitting digit impulses to said control switch, means under control of said control switch in response to two digit impulses to cause one of said selector switches to advance, first to a group of lines and then to a line within said group, the means under control of said control switch comprising electrical connections between contacts in the selector switch and said control switch to which marking poten tials are applied, without moving said control switch to a predetermined position after the first marking operation has terminated.

3. In a telephone exchange system the combination of a plurality of final selector switches provided with banks, a control circuit including an auxiliary switch, means for transmitting tens and units digits impulses to said switch, and means controlled by said control circuit and auxiliary switch in response to the tens and units digit impulses to successively perform two marking operations in the bank of a selector switch.

4. In a telephone exchange system the combination of a pluralitv of final selector switches provided with banks, a control circuit including an auxiliary switch. means for transmitting tens and units digit im-- pulses to said switch, and means controlled by said controlled circuit and auxiliary switch in response to the tens and units digit impulses to successively perform two marking operations in the bank of a selector switch, without advancing to an intermediate or normal position between said two marking operations.

5. In a telephone exchange system the combination of a plurality of selector switches provided with banks to which groups of lines are connected, a control switch common to a plurality of said selector switches, said control switch having two selective movements, a control mechanism, means controlled by said control switch to first mark a group of lines in the banks of a selector and then mark particular line in the group, means controlled by said mechanism for controlling the selective movements of said control switch, and means controlled by said control switch to send revertive impulses to said mechanism. 7

6. In a telephone exchange system the combination of a plurality of selector switches, banks for said switches connected with groups of lines, a control circuit common to said selector switches and provided with a control switch, means for associating said control circuit with anyone of said selector switches, means for advancing said control switch to mark a group of lines in the bank of a selector switch, means for advancing said selector switch to the group of marked lines, means for advancing said control switch to mark a particular line in the group, and means for then advancing said selector switch to said marked line. I

7 In a telephone exchange system the combination of a plurality of selector switches, banks for said switches connected with groups of lines, a control circuit common to said selector switches and provided with a control switch, means for associating said control circuit with any one of said selector switches, means for advancing said control switch to mark a group of lines in the bank of a selector switch, means for advancing said selector switch to the group of marked lines, means for advancing said control switch to mark a particular line in the group, means for then advancing said selector switch to said marked line, and means for thereafter releasing said control circuit for use with another selector switch. I

8. In a telephone exchange system the combination of a plurality of selector switches provided with banks connected to a group of lines, a control circuit common to said selector switches and provided with a control switch, means for causing said control switch to select a selector switch, and means for then causing said control switch to first mark a group of lines in the bank of the selected selector switch and then to mark a particular line in said group.

9. In a telephone exchange system the combination of a plurality of selector switches provided with banks connected to a group pflines, a control circuit common to said selector switches and provided with a control switch, means for causing said control switch to select aselector switch, means for causing v a switch to first mark a group of the bank of the selected selector and then to mark a particular line in said group and means for controlling the operations of said control switch a mechanism to which the control switch sends revertive impulses. :IQQIn a. telephone exchange system the fmbination of a plurality of selector switches provided with banks connected to a' 'gifoup of lines, a. control circuit common said selector switches and provided with ia' control switch, means for causing said contihl switch to select a selector switch, means for causing said control switch to first mark afiltoup of lines in the bank of the selected sol or, switch and then to mark a particular' 'line in said group, said control switch provided with a brush and a bank of groundcontacts, the means for controlling the marking operations of said control switch comprising a mechanism to which revertive impulses are sent from said brush and contacts ll, In

a telephone exchange system the combination of a plurality of selector switches each provided with a relay, a control circuit provided with an auxiliary switch, said control circuit connected in multiple relation to said selector switches, means 'f or causing the operation of said auxiliary switch to select one of said selector switches,

selector switch when selected causing e operation of one of said relays, the optionjof said relay serving to connect said control circuit with the selected selector switch.

L 12; In a telephone exchange system the combination of a selector switch having accessto a group of lines, said selector switch provided with bank contacts, each contact being normally connected to ground, a drivingmagnet for said selector switch, a line relay for each of said lines, a control circuit common to said selector switch, means for operating said relays, the operation of said relaysserving to remove ground from the bank Contacts and the removal of said ground causing the operation of said control circuit 'to reoperate the driving magnet of the sedoctor switch.

.13. In a telephone exchange system the combination of a selector switch provided withbank contacts, an auxiliary switch also provided with bank contacts, connections extending between the bank contacts of said switches, means for causing said auxiliary switch to make two movements, the first movement causing the selector switch to adyance to a group of contacts and the second movement causing the selector switch to advance to a contact in the group, the connections between the bank contacts of the two switches being such that when the control switch makes a maximum movement during its second movement the selector switch makes a minimum movement and vice versa.

14. In a telephone exchange system the combination of a plurality of selector switches for selecting groups of lines, a control switch common to said selector switches, means for transmitting two digit impulses to cause the operation of said control switch, means under control of said control switch for causing said selector switches to first advance to select a group of lines corresponding to the first digit and to a line in the group corresponding to the second digit.

15. In a telephone exchange system the combination of a plurality of conversation switches for selecting groups of lines, a control switch common to said conversation switches and having two selective movements, means controlled by said control switch in its first movement to cause said conversation switches to select a group of lines and in response to the second movement to select a line in the group.

16. In a telephone exchange system the combination of a plurality of conversation switches for selecting groups of lines, a control switch common to said conversation switches and having two selective movements, means controlled by said control switch in its first movement to cause said conversation switches to select a group of lines and in response to the second movement to select a line in the group, a mechanism for controlling both selective movements of said control switch, and means controlled by said control switch for sending revcrtive impulses to said mechanism.

17. In an automatic telephone system a selector switch having a bank of contacts and wipers adapted to engage with said contacts,

an auxiliary switch having a bank of contacts and wipers adapted to engage with said contacts, electrical connections extending between contacts of said auxiliary switch and certain contacts representing the tens groups of said selector switch and other electrical connections extending between contacts of said auxiliary switch and contacts of said selector switch intermediate said certain contacts and representing the units in said tens groups, means for successively moving the wipers of said auxiliary switch in accordance with tens and unit digits and means for moving the wipers of said selector switch into engagement with its bank contact which has been marked by the electrical connections from the auxiliary switch.

18. In a telephone system the combination of a selector switch. an auxiliary switch associated with said selector switch, a plurality of marking wires connecting the bank terminals 01": said selector switch and said auxiliary switch whereof each marking wire extending from a tens group contact in the bank of said selector switch is connected to a plu rality of contacts in the bank of said auxiliary switch whereas the units marking wires extending from single contacts in the bank of the auxiliary switch are connected to a plurality of units contacts in the bank of said selector switch, means for operating said auxiliary switch in accordance with tens and units di it impulses to mark a contact in the bank of said selector switch and means for driving the brushes of said selector switch to said marked contact.

19. In a telephone system the combination of a selector switch, an auxiliary switch associated with said selector switch, a plurality of marking wires connecting the bank terminals of said selector switch and said auxiliary switch, individual lines and groups of private branch exchange lines connected to the bank of said selector switch, means for operating said auxiliary switch in accordance with tens and units digit impulses to mark a contact in the bank of said selector switch, means for driving the brushes of said selector switch to said marked contact and means operative it said marked contact is a busy first line of one of said groups of private branch exchange lines to cause said driving means to drive said brushes over said group of private branch exchange lines to select a tree line within the group.

20. A telephone system according to claim 19 and wherein said auxiliary switch forms part of a control circuit common to a plurality of said selector switches, characterized in this that the cut-off relays of the private branch exchange lines except the last line of each group are adapted when energized to remove the ground from a contact in the bank of the selector switch, the absence of such ground being adapted to effect an operation in said control circuit to cause the reclosure of the circuit of the driving magnet of the selector switch.

21. In a telephone exchange system the combination of a plurality oi selector switches, means for busying one of said switches, a control switch common to said selector switches, a plurality of marking wires connecting bank terminals of said selector switches and said control switch, means for causing said control switch to select the said busy selector switch, and means for causing the said control switch to make a plurality of selective movements to control the said selector switch by marking potentials applied over said marking wires.

22. In a telephone exchange system the combination of a plurality of selector switches, a plurality of auxiliary control switches less in number than said selector switch and each common to a group of said selector switches, marking wires connecting the bank terminals of said control switches and the bank terminals of the selector switches in the respective groups, driving means common to all of said switches, means for operatively connecting any of said switches with said common driving means, means for controlling the movement of said control switches in accordance with the value of received digit impulses, and means for controlling the movement of said selector switches by marking potentials applied over said marking wires. In witness whereof, we hereunto subscribe our names this 19 day of August 1930.

CHARLES EDWARD STEVENS. JOHANNUS CORNELIS SCHOONEMAN.

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